The present invention relates to improvements in magnetic data storage disc drives, and is more specifically related to an improved circuit and method for programming the inductance of read/write heads for read and write operations.
Read/write heads are popular in information recording and retrieval systems such as disc drives. Many information storage systems are designed for both the recording and the retrieval of data, and therefore require both a write and a read head. For example, conventional disc drives are used to both record and retrieve information. It is particularly advantageous to use one head, a read/write head, for both the recording and the retrieval of data. The read/write head is adapted to transfer data between the storage medium and an external system such as a computer's microprocessor.
FIG. 1a is a block diagram of a recording and retrieval system 10, hereinafter disc drive 10. The disc drive 10 contains read/write head 14 connected to a write driver 12 and to a read amplifier 25. The write driver 12 and read amplifier 25 can be on a single integrated chip 70. The read/write head 14 is positioned near a storage medium 8, such as a disc. The disc drive 10 usually has a read/write head both above and below, not shown, the storage medium. The disc drive 10 typically contains logic, such as the controller 29, usually a microcontroller, that controls the operation of disc drive 10. The disc drive 10 may also include various other circuitry, not shown.
FIG. 1b shows a schematic of the disc drive 10, having a conventional read/write head 14. The read/write head 14 is typically an inductor having an inductance L between 400 nH to 600 nH in current technology. The read/write head 14 is connected to a write driver 12 and to the differential inputs 32, 34 of the read amplifier 25 at the base of read transistors 26, 28. The emitters of read transistors 26, 28 are connected to a current source 30. The read/write head 14 is connected in parallel to a damping network 16 and a current clamp 24. The damping network 16 has a pair of diodes 18, 20, in parallel, connected in series with a resistor 22, although any conventional damping network can be used.
The problem with using the same head for both read and write operations is that the requirements for optimal read operations are diametrically opposed to the requirements for optimal write operations. To optimize the read operation the inductance L should be as large as possible. The read back amplitude is a function of the inductance L and a larger inductance L gives a stronger signal during a read operation, which gives greater accuracy in the data read. To optimize the write operation the inductance L should be as small as possible. A smaller inductance allows for a faster rise in current through the head during a write operation, which reduces the transition length on the media, therefore reducing intersymbol interference, such as bit shifts and partial demagnetization.
At best, the value of the inductance L of the read/write head is a compromise between the desire to increase the inductance L to produce the strongest signal for the read operation, and to decrease the inductance L to produce a faster current for the write operation.
To improve both the read and write operations, separate inductive elements can be used for the read and for the write. However, separate inductive elements will greatly increase the cost of the disc drive 10. Of course, cost increases are to be avoided. Furthermore, adding another inductor is particularly difficult because of the manufacturing process for multiple inductors. Additionally, because the head is an inductor and has to be an external component two connectors and two input output pads have to be added to the integrated circuit 70 for every additional head, further increasing the cost of the disc drive 10.
A further problem with using the same head for both read and write operations is that the head is connected to both the inputs of the read amplifier 32, 34 and to the write driver 12. During a write operation, the write driver 12 produces very large voltage swings across the read/write head 14. This can overstress the read amplifier 25.
One way to prevent the large voltage swings across the read/write head 14 from affecting the read amplifier 25 is to connect the current clamp circuitry 24 across the read/write head 14. The current clamp 24 is additional circuitry and increases the cost and size of the disc drive 10. Another way to prevent the large voltage swings across the read/write head 14 from affecting the read amplifier is to use different heads for the read and write operations, however, as described above, this also increases the cost of the integrated circuit 70.